Patent GB-925293-A (GB)
Title: Improvements in servo-assisted braking systems
IPC: B60T8/44
Filed: 1959-09-29
Abstract: 925,293. Fluid-pressure brakes. E. M. ROBINSON. Nov. 10, 1960 [Sept. 29, 1959; Nov. 26, 1959], Nos. 33079/59 and 40161/59. Class 103 (1). [Also in Groups XXIV, XXXI and XXXV] In a servo-assisted braking system, e.g. for aircraft or commercial vehicles, of the kind having a pneumatic servo circuit there is incorporated in the latter a valve operated electrically by means which is supplied with current from a generator associated with a wheel to be braked, the valve functioning to discontinue the servo action when, as a consequence of rapid wheel deceleration such as occurs just prior to wheel locking, there is a sudden fall in generator output current. The system may operate in conjunction with a similar system in which the generator is responsive to sudden acceleration and the valve functions to cause locking of the differential gear of the vehicle. As shown, the servo circuit comprises a pneumatic cylinder 7 containing a piston 6 which is directly connected with the piston 5 of an hydraulic master cylinder 1, there being a pipe 8 connecting the space A with the inlet manifold of the engine of a vehicle to be braked, and a communicating pipe 9 connecting the spaces A and B via a valve V controlled by the pressure of hydraulic fluid to the cylinder 1 such that the portion 11 of pipe 9 is cut-off and space B connected with atmosphere via a pipe 10 when valve V is operated. A further valve IV for discontinuing the servo action (or causing locking of the differential) is incorporated in the pipe 9 to interrupt flow in the latter from pipe 10 and by-pass valve V through a pipe 12. The valve IV is movable from the position shown in Fig. 9 to a raised position in which flow to the valve V from pipe 9 is prevented, the latter then being connected via pipe 12 to the space A. This movement is effected by a solenoid 13 whenever deceleration of a braked wheel at a sufficiently rapid rate occurs, i.e. when the wheel tends to become locked. For this purpose the solenoid is fed with current either directly from a generator associated with the braked wheel or preferably, as shown, from a battery B via a relay R2 having coils 21, 23 fed respectively by windings W, W1 of a generator constructed as shown in Figs. 4 and 6. The windings W, W1 are stationary and are surrounded by a rotating ring of magnets 15. An interference shutter 16 comprising two staggered series of apertures is mounted for limited rotation such that when one series of apertures are aligned with the magnet poles, Fig. 6, so that the flux is largely diverted from one winding through the shutter portions disposed between adjacent poles, the other series of apertures are aligned with the spaces between the poles (Fig. 7, not shown), whereby maximum flux is obtained through the other winding. The shutter is arranged normally to occupy the Fig. 6 position but moves under inertia forces to the other position when the wheel tends to lock. As a result the current through coil 23 is increased and that through coil 21 decreased, thus operating the relay R2 to cause energization of solenoid 13. A second relay R1, having a slow or delayed action, and fed by current from both of the windings W, W1 disconnects the circuit to solenoid 13 and operates a warning light 24 if the wheel slows to a speed at which the generator current is insufficient for proper control of relay R2.